A wiring board may be used for mounting a semiconductor integrated circuit that is operated at high speed. A wiring board equipped with a differential circuit for transmitting a high frequency signal at high speed has been conventionally known. In a wiring board, a pair of differential lines can be configured in the wiring board at predetermined intervals in depth. The pair of differential lines may be electrically connected to a pair of surface layer line conductors provided on the main surface of the wiring board respectively via a pair of penetration conductors (vias) penetrating a thickness direction of the wiring board.
However, the heights of each of the penetration conductors are different from each other because they must penetrate the wiring board to different depths. Signals transmitted through the penetration conductors will travel different distances, and thus will have different transmission delay times (skew). When transmitting a differential signal, the different transmission delay times will cause each of the two signals to be out of phase, and transmission quality is deteriorated.
Accordingly, there is a need for a wiring board equipped with differential lines which reduce signal deterioration.